Light emitting device and fluidic manufacture thereof

ABSTRACT

Light emitting devices and methods for their manufacture are provided. According to one aspect, a light emitting device is provided that comprises a substrate having a recess, and an interlayer dielectric layer located on the substrate. The interlayer dielectric layer may have a first hole and a second hole, the first hole opening over the recess of the substrate. The light emitting device may further include first and second micro LEDs, the first micro LED having a thickness greater than the second micro LED. The first micro LED and the second micro LED may be placed in the first hole and the second hole, respectively.

BACKGROUND

Light emitting devices (LEDs) are anticipated to be used in futurehigh-efficiency lighting applications, such as displays and lights.Recently, micro LEDs have been developed for future high-efficiencylighting applications. One challenge associated with such devices isthat the assembly of micro-scale components can be costly andcomplicated, making it difficult to achieve high assembly accuracy at areasonable manufacturing cost.

Methods for the distribution or alignment of small devices onto atransparent substrate, such as glass or a polymer, to create lightemitting devices are well known in the art. One cost-effective method isfluidic self-assembly, in which a liquid carrier medium of an ink orslurry is filled with small lighting devices, and allowed to flow overthe substrate. The small lighting devices are carried across thesubstrate by fluid transport, and gravity is used to mechanically trapthe small lighting devices in mechanical trapping sites on the substratein the manufacturing process. However, in conventional fluidicself-assembly methods, when small devices with different sizes aretrapped in trapping sites, the devices are often misaligned or disposedin the incorrect sites. Moreover, even when the devices are correctlyaligned and disposed in the correct sites, the resulting surface of thelight emitting device may not be planar, requiring a polishing stepafter assembly, which compromises the cost-effectiveness of themanufacturing process, and in some cases can undesirably alter theprecise positioning of the small lighting devices.

SUMMARY

To address the above issues, light emitting devices and methods fortheir manufacture are provided. According to one aspect, a lightemitting device is provided that comprises a substrate having a recess,and an interlayer dielectric layer located on the substrate. Theinterlayer dielectric layer may have a first hole and a second hole, thefirst hole opening over the recess of the substrate. The light emittingdevice may further include a first and second micro light emittingdevice, the first micro light emitting device having a thickness greaterthan a second micro light emitting device. The first micro lightemitting device and the second micro light emitting device may be placedin the first hole and the second hole, respectively.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Furthermore,the claimed subject matter is not limited to implementations that solveany or all disadvantages noted in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated by way of example and not by wayof limitation in the figures of the accompanying drawings, in which thelike reference numerals indicate like elements.

FIGS. 1A-B show schematic diagrams of a light emitting device accordingto a first embodiment of the present invention.

FIG. 2 shows a schematic diagram of a light emitting device according toa second embodiment of the present invention.

FIGS. 3A-B show schematic diagrams of a light emitting device accordingto a third embodiment of the present invention.

FIG. 3C shows a schematic diagram of a light emitting device accordingto a fifth embodiment of the present invention.

FIGS. 4A-H show an overview of the process for producing a lightemitting device in accordance with the first embodiment of the presentinvention.

FIGS. 5A-B show schematic diagrams of a self-alignment process forproducing a light emitting device in accordance with the firstembodiment of the present invention.

FIG. 6 shows an overview of a modified process for producing a lightemitting device in accordance with the first embodiment of the presentinvention.

FIGS. 7A-B show schematic diagrams of a light emitting device accordingto a fourth embodiment of the present invention.

DETAILED DESCRIPTION

Selected embodiments of the present invention will now be described withreference to the accompanying drawings. It will be apparent to thoseskilled in the art from this disclosure that the following descriptionsof the embodiments of the invention are provided for illustration onlyand not for the purpose of limiting the invention as defined by theappended claims and their equivalents.

Referring initially to FIG. 1A, a light emitting device 10 is providedaccording to the first embodiment of the present invention. FIG. 1Ashows a cross-sectional view of a light emitting device 10 (referred toalternatively herein as “LED”). The light emitting device 10 comprises asubstrate 20 having a recess 30, an interlayer dielectric layer 40 beinglocated on the substrate 20, and having a first hole 22 and a secondhole 24, the first hole 22 opening over the recess 30 of the substrate20 so as to communicate with the recess 30. The light emitting device 10may further comprise a third hole 26 in the interlayer dielectric layer40 having a different size from the second hole 24. Typically, the firsthole 22, second hole 24, and third hole 26 have different sizes fromeach other. Numerous shapes are possible for the cross sections of theholes, and numerous dimensions are possible for the different sizes ofthe holes. In one specific example, the first hole 22, second hole 24,and third hole 26 may be configured in circular shapes with diameters ofbetween 95 and 115 μm, between 70 and 90 μm, and between 45 and 65 μm,respectively. And, in one more specific example the respectivedimensions may be 105 μm, 80 μm, and 55 μm. Typically, the effectivediameter of the holes are sized to be a few microns (e.g., 1-6 μm, andmore typically 3 μm) larger than the corresponding micro LEDs to allowthe micro LEDs to fit within the holes without being too easilydislodged. With this configuration, the holes are configured tomechanically trap micro LEDs of different sizes during fluid transportin the manufacturing process, as explained in more detail below.

In FIG. 1A, the third hole 26 is delineated on the top and bottom bydotted lines A and B, respectively, and the recess 30 is delineated onthe top by dotted line B. Dotted line A represents an imaginary planethat extends over the first hole 22 along the plane of the upper surfaceof the interlayer dielectric layer 40, while dotted line B represents animaginary plane delineating the boundary between the first recess 30 andthe first hole 22, extending over the first recess 30 along the plane ofthe upper surface of the substrate 20. In the depicted embodiment, thedepth of the recess 30 is configured to be substantially equal to athickness of the interlayer dielectric layer 40, although it will beappreciated that other configurations are possible and the recess 30 maybe shallower or deeper than the thickness of the interlayer dielectriclayer 40, with the total thickness of the recess 30 and first hole 22being selected to match the thickness of a corresponding micro LED, asdescribed below. Accordingly, a trapping site is created that canselectively trap larger devices. The first hole 22, second hole 24, andthird hole 26 may be configured with thicknesses that are substantiallyequal to the thickness of the interlayer dielectric layer 40. In anexample configuration, the thickness of the interlayer dielectric layer40 may be selected to be between 0.1 and 100 μm, and more specificallymay be selected to be between 1 and 50 μm, and in one particularembodiment may be 5 μm. In FIG. 1A, it will be appreciated that themicro LEDs have been removed for illustrative purposes.

The recess 30 is provided on the upper surface of the substrate 20,which is preferably a transparent substrate that may comprise or beformed of a plastic, polymer (polyimide, for example), or glass(perforated glass, quartz glass, or sapphire glass, for example). Thetransparent substrate may alternatively be a laminated sheet comprisinga substrate having two layers. A depth of the recess 30 is typicallyselected to be between 0.1 and 100 μm, and more specifically may bebetween 1 and 50 μm, and in one particular embodiment may be 5 μm. Therecess 30 may be configured in a shape and dimension that corresponds tothe first hole 22, which in one specific example may be a circular shapewith a diameter of between 95 and 115 μm, or more specifically of 105μm. Alternatively, the recesses 30 could be embossed or etched to havedifferent depths on the same substrate 20 to accommodate micro LEDdevices of different depths.

The interlayer dielectric layer 40, typically located on the uppersurface of the substrate 20, comprises a polymeric material such as anacrylic resin or a polyimide resin in this embodiment, but may alsocomprise a silicon nitride (SiNx) or a silicon oxide (SiO) instead. Athickness of the interlayer dielectric layer 40 may be configured torange between 0.1 and 100 μm, and more specifically between 1 and 50 μm.

Referring to FIG. 1B, the micro LEDs are depicted in the holes andrecess 30 to illustrate the final assembly of the light emitting device10. A first micro LED 12 has a thickness greater than a second micro LED14 and is placed in the first hole 22, and the second micro LED 14 islocated in the second hole 24. A third micro LED 16 may be located inthe third hole 26 and may have a different size from the second microLED 14. The first micro LED 12 and second micro LED 16 may be providedon the light emitting device 10, such that an upper surface of theinterlayer dielectric layer 40, an upper surface of the first micro LED12, and an upper surface of the second micro LED 14 are substantiallylevel, obviating the need to planarize the upper surface of the lightemitting device 10 following assembly by using a polishing process, suchas CMP, or by adding additional layers, etc. In this manner, coverlayers such as optical films, etc., may be easily manufactured on alevel surface over the light emitting device 10. The first hole 22 andsecond hole 24 are respectively configured to be slightly larger thantheir corresponding micro LEDs, namely, first micro LED 12 and secondmicro LED 14. For example, the diameters of the micro LEDs areconfigured so that the first hole 22, second hole 24, and third hole 26have diameters that are a predetermined distance, such as 5 μm, largerthan the first micro LED 12, second micro LED 14, and third micro LED16, respectively, allowing the micro LEDs to easily settle into theirrespective holes during fluidic transport assembly, as described below.Alternatively, in another embodiment, the upper surfaces of the firstmicro LED 12, second micro LED 14, and third micro LED 16 may be lowerthan the upper surface of the interlayer dielectric layer 40, and asubsequent planarization process may be applied, if desired, toplanarize the upper surface of the assembly, for example, by addingmaterial on top of the micro LEDs or by removing material on the uppersurface of the interlayer dielectric layer 40.

Like the holes 22, 24, 26 described above, it will be appreciated thatthe first micro LED 12, the second micro LED 14, and the third micro LED16 also have different sizes, and these different sizes may be expressedin terms of the differences in their respective upper surface areas. Forexample, an area of the upper surface of the first micro LED 12 islarger than an area of the upper surface of the second micro LED 14, andwhich in turn is larger than an area of the upper surface of the thirdmicro LED 16. As an example of the degree to which the upper surfacesareas may vary, the area of the upper surface of the second micro LED 14and the corresponding upper opening of the second hole 24 may be atleast 1.2 times larger than the upper surface of the third micro LED 16and the corresponding upper opening of the third hole 26, and morespecifically may be over 1.5 times larger. It will be appreciated thatit is desirable to obtain uniform perceived brightness among the microLEDs, and accordingly these exemplary differences in dimensions arebased upon differences in the emissions intensities in each type ofmicro LED, and also account for manufacturing process margins, cost, andother factors. Regarding the shape of the micro LEDs, in the depictedembodiment, the micro LEDs are configured in cylindrical shapes. In oneparticular arrangement, the first micro LED 12 may have a 100 μmdiameter, the second micro LED 14 may have a 75 μm diameter, and thethird micro LED 16 may have a 50 μm diameter. It will be appreciated,however, that the diameters may range between 1 and 1000 μm. It will beappreciated that due to the size differences described above, the microLEDs can be self-assembled through fluidic transport in successive wavesin which the largest type of micro LED is first transported and fills upavailable sites, the next largest type of micro LED is next transportedand fills up available mid-sized sites, and finally the smallest type ofmicro LED is transported and fills the remaining sites, to achieve aplanar upper surface on the light emitting device 10 with substantiallyall sites filled, without requiring the use of polishing methods, suchas CMP, or additive leveling methods after assembly.

The first micro LED 12, second micro LED 14, and third micro LED 16 maybe configured to emit red, green, and blue light, respectively, andtogether may function as a pixel that emits blended light of a desiredcolor and intensity. The red micro LED generally may be gallium arsenidebased, and as a result may be thicker than the blue and green microLEDs, which may be gallium nitride based. The red micro LED typicallyhas a weaker emission intensity per unit area, so the red micro LED ismay be configured to have a larger emission area to compensate andthereby achieve similar emission intensities as the other micro LEDs. Inthis way, the thicknesses and areas of the micro LEDs may vary. Asexample thicknesses, the thickness of the first micro LED 12 may begreater than the thicknesses of the second micro LED 14 and the thirdmicro LED 16, respectively. In one particular embodiment, the firstmicro LED 12 may have a 10 μm thickness, the second micro LED 14 mayhave a 5 μm thickness, and the third micro LED 16 may have a 5 μmthickness, although variations of these thicknesses are possible. Thisparticular configuration of the thicknesses allows the upper surface ofthe interlayer dielectric layer 40 and the upper surfaces of the firstmicro LED 12, second micro LED 14, and third micro LED 16 to besubstantially level without the need to apply a polishing process, suchas a CMP process, to planarize the upper surface of the light emittingdevice 10.

The first micro LED 12, second micro LED 14, and third micro LED 16 haveupper surfaces configured as light emitting faces emitting known peakspectra, and back surfaces configured as connecting electrodes. Forexample, the first micro LED 12 may comprise aluminum gallium indiumphosphide (AlGaInP) with a peak spectrum of 630 nm (red), the secondmicro LED 14 may comprise indium gallium nitride (InGaN) with a peakspectrum of 517 nm (green), and the third micro LED 13 may comprisegallium nitride (GaN) with a peak spectrum of 460 nm (blue).

By providing such a light emitting device 10 as shown in the firstembodiment, which includes the recess 30 of the substrate 20, and theinterlayer dielectric layer 40 having a first hole 22 and a second hole24, the first hole 22 opening over the recess 30 of the substrate 20, afirst micro LED 12 having a thickness greater than a second micro LED14, and the first micro LED 12 and the second micro LED 14 being placedin the first hole 22 and the second hole 24, respectively, LEDs ofdifferent thickness may be easily and surely positioned on the substrate20, so that a planar upper surface is achieved on the light emittingdevice 10 without the use of polishing methods after assembly, such asCMP, or additive leveling.

Referring to FIG. 2, a light emitting device 110 is provided accordingto the second embodiment of the present invention. FIG. 2 shows amagnified, cross-sectional view of a light emitting device 110 in thevicinity of the first micro LED 112. In the light emitting device 110 ofthe second embodiment, the recess 130 of the substrate 120 may have atapered shape, as viewed in cross section, and the first hole 122 in theinterlayer dielectric layer 140 also has a tapered shape as viewed incross section. In FIGS. 2, T1 and T2 are the taper angles, relative tohorizontal, of the recess 130 and first hole 122 respectively. T3 is thetaper angle, relative to horizontal, of the first micro LED 112. In thedepicted embodiment, T3 is the same as T1 and T2, but it will beappreciated that T3 may differ from T1 and/or T1. For example, therecess 130 and the first hole 122 may be tapered at a 30 to 60 degreeangle relative to a horizontal orientation, such that angles T1 and T2are formed at angles between 30 and 60 degrees. In a more specificembodiment, the angles T1 and T2 may be formed at 45 degrees, asdepicted. While T1 and T2 are illustrated as being the same value in thedepicted embodiment, it will be appreciated that each of T1 and T2 maybe a different angle that is formed within the range of 30 to 60degrees, for example. In one specific alternative embodiment, the firsthole 122 in the interlayer dielectric layer 140 has no taper (T2=90degrees) while the recess is tapered such that T1 is between 70 and 85degrees, and the first micro LED 112 has a taper of between 70 and 85degrees such that T1=T3. The tapered structures help orient electrodesand micro LEDs to align properly as the micro LEDs are fluidicallytransported over the holes, and settle into the holes under theinfluence of gravity.

Although only illustrated as a cross section in FIG. 2, it will beappreciated that the shape of the first micro LED 112 may be a discshape or a polygonal shape such as an octagon or hexagon, and havetapered sides that are configured similarly to the tapered recess andhole described above. Due to the tapered sides, an area of the lightingsurface 112 a (i.e., upper surface) is larger than an area of anelectrode surface 112 b (i.e., bottom surface) of the first micro LED112. Thus, the first micro LED 112, located in the first hole 122 andrecess 130, is configured in a shape that allows it to fit easily intothe first hole 122 and the recess 130. While only a single tapered hole122 and single tapered micro LED 112 are shown in the light emittingdevice 110 of FIG. 2, it will be appreciated that this is forillustrative purposes to describe the possibility of tapered sides, andthat all or a selected plurality of the holes, recesses, and micro LEDsin the other embodiments described herein may be formed with a tapersimilar to that shown in FIG. 2 to encompass various permutations,including an embodiment where only the holes are tapered and the microLEDs are not tapered. Thus, a second micro LED and a third micro LED,and their corresponding holes, described below, may have a similarstructure as the first micro LED 112. The disc-shape or polygon-shapedescribed above aids in inhibiting the micro LEDs from aggregatingtogether as a mass during fluid transport of the micro LEDs during themanufacturing process, thereby promoting their distribution across anentire substrate and quick settling into the holes distributed acrossthe substrate.

Referring to FIG. 3A, a top plan view of a dot-pattern area 244 of alight emitting device 210 of the third embodiment is illustrated, whichmay also be referred to as a pixel. It will be appreciated that thelight emitting device 210 may comprise a plurality of such dot patternsas embodied by the dot-pattern area 244, for example arranged in rowsand columns as a grid or other repeating pattern as a display,television, ceiling light, car light, etc. The light emitting device 210of this embodiment has four micro LEDs configured within the dot-patternarea 244, comprising the first micro LED 212 which is configured to emitred light, the second micro LED 214 which is configured to emit greenlight, the third micro LED 216 which is configured to emit blue light,and a fourth micro LED 218 which is also configured to emit blue light.The configuration of two blue micro LEDs in the dot-pattern area 244 isintended to improve the color gamut by accounting for the fact thatspectral sensitivity in humans is generally weaker at shorterwavelengths (in humans, spectral sensitivity is identified at threepeaks roughly corresponding to red, green, and blue, respectively; thestrongest peak is green, followed by red and blue). The third micro LED216 and fourth micro LED 218 may not necessary have the same peakspectrum. For example, the third micro LED 216 may comprise GaN with apeak spectrum of 450 nm, and the fourth micro LED 218 may comprise GaNwith a peak spectrum of 470 nm.

Like the first embodiment, the four micro LEDs depicted in FIG. 3A areconfigured in cylindrical shapes, although other shapes may be used. Inone specific example, the first micro LED 212 may have a diameterbetween 90 and 110 μm, such as 100 μm, the second micro LED 214 may havea diameter between 65 and 85 μm, such as 75 μm, and the third and fourthmicro LEDs 216, 218 may have a diameter between 40 and 60, such as 50μm, for example. As discussed above, the red micro LED is oftenconfigured to be thicker than the green or blue micro LEDs due to itsconstituent materials. Thus, the thickness of the first micro LED 212 istypically configured to be thicker than the second, third, and fourthmicro LEDs 214, 216, 218. Thus, in one specific example, the first microLED 212 may have a thickness between 8 and 12 μm, such as 10 μm, thesecond micro LED 214 may have a thickness between 4 and 6 μm, such as 5μm, and the third and fourth micro LEDs 216, 218 may have a thicknessbetween 4 and 6 μm, such as 5 μm.

Referring to FIG. 3B, a top plan view of the electrodes 242 a, 242 b,and 242 c in the dot-pattern area 244 of the light emitting device 210is illustrated. The micro LEDs have been removed in this drawing forillustrative purposes. The first hole 222, second hole 224, third hole226, and fourth hole 228 are located in the interlayer dielectric layer240. The first electrode 242 a is configured to electrically contact anelectrode surface of the first micro LED 212 placed in the first hole222, the second electrode 242 b is configured to electrically contact anelectrode surface of the second micro LED 214 placed in the second hole224, and the third electrode 242 c is configured to electrically contactelectrode surfaces of both the third micro LED 216 placed in the thirdhole 226 and fourth micro LED 218 placed in the fourth hole 228. Thefirst electrode 242 a, second electrode 242 b, and third electrode 242 cdo not intersect each other. The third electrode 14 c is shaped in azigzag pattern to avoid contact with the first micro LED 212 or thesecond micro LED 214 and their respective electrodes.

In this embodiment, the interlayer dielectric layer 240 not onlyisolates the electrodes 242 a, 242 b, and 242 c for the micro LEDs, butalso provides holes that serve to selectively trap disposed deviceswhile excluding larger devices. Solder or eutectic contact may be reliedupon to ensure good electrical contact between the electrodes and thedisposed devices. Solder may also be liquid during assembly and providecapillary force interaction with devices to aid in trapping.

Referring to FIG. 3C, a top plan view of a dot-pattern area 444 (i.e., apixel) of a light emitting device 410 of the fifth embodiment isillustrated, in which the sizes of each of the holes formed therein forthe associated micro LEDs have been adjusted as compared to theembodiment of FIGS. 3A and 3B to account for human spectral sensitivity.As with the third embodiment, it will be appreciated that the lightemitting device 410 may comprise a plurality of such dot patterns asembodied by the dot pattern area 444. The micro LEDs have been removedin this drawing for illustrative purposes. The first holes 422 a-b,second holes 424 a-c, and third holes 426 a-d are located in theinterlayer dielectric layer 440. The first top lead electrode 442 d andfirst bottom lead electrode 442 a are configured to electrically contactelectrode surfaces of the red micro LEDs that are placed in the firstholes 422 a-b, thereby forming the red sub-pixel. The second top leadelectrode 442 e and second bottom lead electrode 442 b are configured toelectrically contact electrode surfaces of the green micro LEDs that areplaced in the second holes 424 a-c, thereby forming the green sub-pixel.The third top lead electrode 442 f and third bottom lead electrode is442 a are configured to electrically contact electrode surfaces of theblue micro LEDs that are placed in the third holes 426 a-d, therebyforming the blue sub-pixel. The top lead electrodes 442 d-f and bottomlead electrodes 442 a-c do not form electrical connections where theyintersect each other, but electrically contact the micro LEDs. It willbe appreciated that each micro LED is configured with two electricalleads: one to electrically connect with a top lead electrode and anotherto electrically connect with a bottom lead electrode. In thisembodiment, the first micro LEDs placed in the first holes 422 a-b mayhave a diameter between 20 and 75 μm, such as 45 μm, the second microLEDs placed in the second holes 424 a-c may have a diameter between 40and 100 μm, such as 70 μm, and the third micro LEDs placed in the thirdholes 426 a-d may have a diameter between 50 and 200 μm, such as 100 μm,for example. As discussed below, it will be appreciated that duringfluidic assembly, the largest diameter micro LEDs are transported afirst stage to fill the largest diameter holes, followed by the secondlargest in a second stage, and then followed by the third largest in athird stage. The total micro LED area for all LEDs in the blue, red, andgreen sub-pixels may be set to have ratio of 6:3:2 (for blue:red:green).The depths for the holes 422 a-b containing the red micro LEDs aretypically deeper than the holes 424 a-c, 426 a-d for the blue and greenmicro LEDs, to accommodate thicker red micro LEDs, and thus of theseholes only holes 422 a-b have a cross sectional structure including arecess extending into the substrate, similar to recess 30 in theembodiment of FIG. 1A, discussed above. The red micro LEDs that areinserted into this embodiment are manufactured with aluminum galliumindium phosphide (AlGaInP) while the blue and green LEDs are based ongallium nitride (GaN) with different amounts of indium doping. Thethicknesses of the blue and green micro LEDs are the same at about 5 μm,while the red micro LEDs are around 10 μm thick or greater. Of course,these are merely exemplary measurements, and LEDs of other dimensionsmay utilized. It will be appreciated that human vision on average ismost sensitive to green light, followed by red light, and is leastsensitive to blue light. Accordingly the size, location, and number ofthe micro LEDs in this embodiment have been adjusted to achieve the sameor similar luminance for each color of sub-pixel, accounting for thevariance in luminous intensity per unit area of the LEDs themselves andvariance in human vision sensitivity to the wavelengths of red, blue andgreen light emitted by each sub-pixel.

FIGS. 4A-F are views in cross section illustrating manufacturing stepsof an example method for producing the light emitting device 10 of FIGS.1A-B, in accordance with the first embodiment of the present invention.

FIGS. 4A-B show the situation when the substrate 20 is formed over abase (for the sake of brevity, the base is omitted in the Figures). Aresist layer 46 is deposited over the substrate 20 as a mask layer,patterned to predetermined patterns by photolithography, and etched bywet etching or embossed to form a recess 30 on the substrate 20. Thedepth of the recess 30 formed in the substrate 20 is configured to besubstantially equal to a thickness (i.e., depth) of the first hole 22 inthe interlayer dielectric layer 40. Accordingly, a trapping site thatcan selectively trap larger devices is created. The resist layer 46 issubsequently removed by ashing or dissolution.

FIG. 4C shows the situation when electrodes 42 are formed on thesubstrate 20 with a recess 30. The electrodes 14 may comprise a metal,such as aluminum, copper, or ITO (Indium Tin Oxide). The electrodes 14can be formed by sputtering, plating, and lift-off methods, for example.The electrodes 14 make electrical connections with the electrodesurfaces of the micro LEDs that are correctly disposed and alignedinside their respective holes. It will be appreciated that theelectrodes 14 are configured to be thin relative to the micro LEDs, sothat the thickness of the electrodes 14 does not interfere with thedisposition and alignment of the micro LEDs inside their respectiveholes. To further improve the electrical connections of the electrodes14 with the electrode surfaces of the micro LEDs, the electrodes 14 maybe formed within dedicated recesses that are provided in the substrate20.

FIG. 4D, shows the situation when the interlayer dielectric layer 40 isprovided over the substrate 20. A first hole 22 is created in theinterlayer dielectric layer 40, opening over the recess 30 of thesubstrate 20, exposing at least a part of the electrode 14. A secondhole 24 and third hole 26 are created in the interlayer dielectric layer40 at predetermined positions, exposing at least a part of theelectrodes 14. The interlayer dielectric layer 40 may comprisephotosensitive resin, which may be separately deposited onto thesubstrate 20 or manufactured from a portion of the substrate 20 througha treatment process.

FIGS. 4E-F depict the first fluid transport stage. It will beappreciated that larger, heavier devices are generally fluidicallytransported in the first fluid transport stage, while smaller, lighterdevices are fluidically transported in subsequent stages with largerdevices filling larger trapping sites first and passing over smallerempty trapping sites, and smaller devices subsequently filling smallertrapping sites. In the first fluid transport stage, the first micro LED12 is fluidically transported to the first hole 22. The left side of thedrawing represents the upstream portion of the fluid flow path,represented by the dark arrows, along which the micro LEDs arefluidically transported, while the right side of the drawing representsthe downstream portion. However, it will be appreciated that theupstream portion and the downstream portion may be designated at othersites on the light emitting device 10 relative to the holes and thesubstrate 20. First, the first micro LED 12 is transferred into a fluidto form an ink or slurry. The slurry is then dispensed over the uppersurface of the substrate 20 and the interlayer dielectric layer 40 atthe upstream portion. The flow speed of the first fluid transport stagemay be a sustained speed of 5 to 200 μm/sec locally at the surfaceduring a low velocity trapping period of the first fluid transportstage, where the first micro LED 12 is disposed into the first hole 22by gravity-driven fluid transport in a downstream direction (see FIG.4F). The flow may also oscillate or pulse at high amplitudes (e.g.,greater than 1 mm/sec) during a distribution period of the first fluidtransport stage in which the LEDs are distributed across the surface,provided there is also the low-velocity trapping period during which theLEDs are allowed to settle. At high flow-entrained disc speeds (e.g.,disc speeds that exceed approximately 200 μm/s), the first micro LED 12may fail to self-align into the first hole 22 and recess 30, or othercomponents (the second micro LED 14 or the third micro LED 16, forexample) may be disposed into the first hole 22 instead of the firstmicro LED 12. It will be appreciated that the disc speed at whichself-alignment may fail to occur is influenced by the disc and wellsize. Further, the relationship between the disc speed and fluid flowspeed is influenced by the properties of the transport fluid.Accordingly, disc speeds ranging from 5 to 100 μm/s locally at thesurface improve the alignment and disposition of the first micro LED 12in the first hole 22. It will be appreciated that the first fluidtransport stage may be repeated multiple times in one manufacturingprocess at variable flow speeds and directions.

FIGS. 4G-H depict the second and third fluid transport stages,respectively. In the second fluid transport stage, the second micro LED14 is fluidically transported to the second hole 24. In the third fluidtransport stage, the third micro LED 16 is fluidically transported tothe third hole 26. The left side of the drawing represents the upstreamportion of the fluid flow path, represented by the dark arrows, alongwhich the micro LEDs are fluidically transported, while the right sideof the drawing represents the downstream portion. However, it will beappreciated that the upstream portion and the downstream portion may bedesignated at other sites on the light emitting device 10 relative tothe holes and the substrate 20. In the second fluid transport phase, thesecond micro LED 14 is initially transferred into a fluid to form an inkor slurry. Likewise, in the third fluid transport phase, the third microLED 16 is initially transferred into a fluid to form an ink or slurry.The slurry is then dispensed over the upper surface of the substrate 20and the interlayer dielectric layer 40 at the upstream portion. It willbe appreciated that the second and third fluid transport stages may berepeated multiple times in one manufacturing process at variable flowspeeds and directions.

The flow speed of the second fluid transport stage may be a sustainedspeed of 5 to 100 μm/s during a trapping period of the second fluidtransport stage, where the second micro LED 14 is disposed into thesecond hole 24 by fluid transport in a downstream direction, andcomponents other than the second micro LED 14 are dislodged from thesecond hole 24. Higher speeds such as 1 mm/s may be used during adistribution period of the second fluid transport stage, to distributethe LEDs of that stage across the surface for settling. For example,FIG. 5A depicts a situation where fluid transport dislodges the thirdmicro LED 16 from the second hole 24. At flow-entrained disc speeds thatexceed 100 μm/s, the second micro LED 14 may fail to self-align into thesecond hole 24, or other components may be disposed into the second hole24 instead of the second micro LED 14. For example, FIG. 5B depicts asituation where the third micro LED 16 is disposed in the second hole 24instead of the second micro LED 14. Accordingly, sustained flow speedsranging from 5 to 100 μm/s improve the alignment and disposition of thesecond micro LED 14 in the second hole 24, while worsening the alignmentand disposition of other components in the second hole 24, especiallywhen the slurry includes various components that are dispensed in thesame transport stage. It is thought that, at certain flow speeds,sufficient turbulence is generated between the gaps within a hole inwhich a mismatched component is disposed so that the mismatchedcomponent is dislodged from the hole. At the same time, if a terminalportion of the mismatched component protrudes from the hole, theinterruption of laminar flow along the surface of the LED could generatesufficient turbulence to exert upward force against the terminal portionof the mismatched component, thereby dislodging the component from thehole. It will be appreciated that, likewise, the third micro LED 16 istransported at a flow speed within a range (5 to 100 μm/s sustained, forexample) that allows it to self-align into the third hole 26. To accountfor the heavier mass of the first micro LED 12 relative to the secondmicro LED 14 and the third micro LED 16, the flow speed of the firstfluid transport stage may be configured to be faster than the flowspeeds of the second and third fluid transport stages. Accordingly, thefluidic self-assembly of the first micro LED 12 is possible despite itsheavier mass relative to the second micro LED 14 and third micro LED 16.It will be appreciated that other processes may be simultaneouslyutilized during the fluid transport stages to affect the fluid transportof the micro LEDs, such as various scattering techniques to help evenlydistribute the micro LEDs during fluid transport. Following assembly,the ink or slurry is subsequently removed from the light emitting device10 through a process such as evaporation.

By the sequential batch assembly method described above, large devicescan be located in larger holes while being prevented from trapping insmaller wells. Subsequently, smaller devices can then assemble in theircorresponding holes while being excluded from larger holes and smallerholes by previously assembled larger devices and size exclusion of theholes, respectively. In this manner, multiple device types may beassembled onto a single substrate with a resulting flat topology thatfacilitates downstream processing and integration without requiring CMPor the overuse of polymeric leveling layers, so that the use of polymers(such as polyimide) can be restricted to patterning electrical contacts,securing and protecting devices, and bridging gaps between the recessesand the micro LEDs.

FIG. 6 is a view in cross section illustrating manufacturing steps of amodified example method for producing the light emitting device 10 ofFIGS. 1A-B, in accordance with the first embodiment of the presentinvention. Like FIGS. 4G-H, the left side of the drawing represents theupstream portion of the fluid flow path, represented by the dark arrows,along which the micro LEDs are fluidically transported, while the rightside of the drawing represents the downstream portion. However, it willbe appreciated that the upstream portion and the downstream portion maybe designated at other sites on the light emitting device 10 relative tothe holes and the substrate 20. FIG. 6 shows a modified second fluidtransport stage in which the second micro LED 14 is fluidicallytransported to the second hole 24, and the third micro LED 16 isfluidically transported to the third hole 26. In essence, the modifiedsecond fluid transport stage combines the second fluid transport stageand the third fluid transport stage, as depicted in FIGS. 4G-H, into onestage. In the modified second fluid transport phase, the second microLED 14 and the third micro LED 16 are initially transferred into a fluidto form an ink or slurry. The slurry is then dispensed over the uppersurface of the substrate 20 and the interlayer dielectric layer 40 atthe upstream portion. As described in FIGS. 4G-H, the flow speeds of themodified second fluid transport stage may be configured within a rangethat allows the second micro LED 14 and the third micro LED 16 toproperly self-align into the second hole 24 and the third hole 26,respectively.

Referring to FIG. 7A, a light emitting device 310 is provided accordingto the fourth embodiment of the present invention. Since the structureof the fourth embodiment is generally similar to the first embodiment,the detailed description thereof is abbreviated here for the sake ofbrevity. It is to be noted that like parts are designated by likereference numerals throughout the detailed description and theaccompanying drawings. FIG. 7A shows a cross-section view of a lightemitting device 310. The substrate 320 of this embodiment has a firstthrough hole 332 formed at a bottom of the recess 330 and opening tocommunicate with the corresponding first hole 322 opening over therecess 330 of the substrate 320. The substrate 320 also has a secondthrough hole 334, formed at a bottom of the second hole 324 in theinterlayer dielectric layer 340, which is not positioned over the recess330. A third through hole 336 is also provided on the substrate 320,formed at a bottom of the third hole 326 in the interlayer dielectriclayer 340.

The method described above for manufacturing a light emitting device maybe modified, so as to manufacture the light emitting device 310, byfurther comprising forming a plurality of through holes (first throughhole 332, second through hole 334, and third through hole 336), each ofthe through holes corresponding to one of the first hole 322 and secondhole 324 of the interlayer dielectric layer 340. The first through hole332 is configured to have a larger width than the second through hole334, which in turn has a larger width than the third through hole 336.After forming the recess 330 of substrate 320, the first through hole332, second through hole 334, and third through hole 336 are formed inthe substrate 320 by etching. The first through hole 332, formed at abottom of the recess 330, is predetermined at the first hole 322 in theinterlayer dielectric layer 340. The second through hole 334 and thirdthrough hole 336 are formed in the substrate 320, which arepredetermined in the interlayer dielectric layer 340 at the bottom ofthe second hole 324 and third hole 326, respectively.

The first through hole 332, second through hole 334, and third throughhole 336 are configured to draw a portion of the transport fluid in thefirst fluid transport stage or the second fluid transport stage. In thefirst fluid transport stage, a vacuum apparatus (not shown) draws aportion of transport fluid through the first through hole 332 to drawthe first micro LED 312 into the first hole 322 and the recess 330 byfluid transport. At same time, the vacuum apparatus also draws particlesthrough the second through hole 334 and the third through hole 336. Itwill be appreciated that the micro LEDs are very small and thin andsometimes break during or prior to the manufacturing process. Thus,broken pieces of the first micro LEDs can form the particles that passthrough the through hole 332.

In the second fluid transport stage, a vacuum apparatus draws a portionof transport fluid through the second through hole 334 and third throughhole 336 to draw the second micro LED 314 and third micro LED 316 intothe second hole 324 and third hole 326, respectively, by fluidtransport. At same time, the vacuum apparatus also draws particlesthrough the first through hole 332. The particles may include brokenpieces of the second micro LEDs 314 and the third micro LEDs 316. Theink or slurry is subsequently removed from the light emitting device 310through a process such as evaporation.

Accordingly, the inclusion of through holes at each assembly site couldremove debris, such as ink impurities or device fragments. If sizedappropriately, the through holes combined with the holes and recessesmay enable the simultaneous and selective self-assembly of micro LEDs,potentially simplifying and shortening the assembly process, as well asenabling the reuse of captured, undisposed devices.

It will be understood that the configurations and/or approachesdescribed herein are exemplary in nature, and that these specificembodiments or examples are not to be considered in a limiting sense,because numerous variations are possible. The specific routines ormethods described herein may represent one or more of any number ofprocessing strategies. As such, various acts illustrated and/ordescribed may be performed in the sequence illustrated and/or described,in other sequences, in parallel, or omitted. Likewise, the order of theabove-described processes may be changed.

The subject matter of the present disclosure includes all novel andnonobvious combinations and subcombinations of the various processes,systems and configurations, and other features, functions, acts, and/orproperties disclosed herein, as well as any and all equivalents thereof.

1. A light emitting device comprising: a substrate having a recess; aninterlayer dielectric layer being located on the substrate, and having afirst hole and a second hole, the first hole opening over the recess ofthe substrate; a first micro light emitting device and a second microlight emitting device, the first micro light emitting device having athickness greater than the second micro light emitting device and beingplaced in the first hole; and the second micro light emitting devicebeing located in the second hole.
 2. The light emitting device of claim1, wherein an upper surface of the interlayer dielectric layer, an uppersurface of the first micro light emitting device, and an upper surfaceof the second micro light emitting device are substantially level. 3.The light emitting device of claim 1, further comprising: a third holein the interlayer dielectric layer having a different size from thesecond hole; and a third micro light emitting device having a differentsize from the second micro light emitting device and being located inthe third hole.
 4. The light emitting device of claim 3, wherein thesecond hole and the second micro light emitting device are at least 1.2times larger than the third hole and the third micro light emittingdevice, respectively.
 5. The light emitting device of claim 3, whereinthe first hole, the second hole, and the third hole have differentsizes, and the first micro light emitting device, the second micro lightemitting device, and the third micro light emitting device havedifferent sizes.
 6. The light emitting device of claim 5, wherein thefirst, second, and third micro light emitting devices are configured toemit red, green, and blue light, respectively, and wherein the thicknessof the first micro light emitting device is greater than the thicknessesof the second and third micro light emitting devices, respectively. 7.The light emitting device of claim 6, wherein an area of the uppersurface of the first micro light emitting device is larger than an areaof the upper surface of the second micro light emitting device, andwhich in turn is larger than an area of the upper surface of the thirdmicro light emitting device.
 8. The light emitting device of claim 6,further comprising: a fourth hole in the interlayer dielectric layer;and a fourth micro light emitting device being located in the fourthhole, which is configured to emit blue light.
 9. The light emittingdevice of claim 1, wherein a depth of the recess in the substrate issubstantially equal to a thickness of the interlayer dielectric layer.10. The light emitting device of claim 1, further comprising: thesubstrate having a first through hole formed at a bottom of the recessand opening to communicate with the corresponding hole first holeopening over the recess of the substrate, and having a second throughhole formed at a bottom of the second hole that is not positioned overthe recess.
 11. The light emitting device of claim 1, wherein a shape ofthe light emitting device is a disc-shape with an area of a lightingsurface larger than an electrode surface, or a polygon-shape with anarea of a lighting surface larger than an electrode surface.
 12. Thelight emitting device of claim 1, wherein the recess of the substratehas a tapered-shape.
 13. The light emitting device of claim 1, whereinthe first and second holes are slightly larger than the correspondingfirst and second micro light emitting devices, respectively. 14-20.(canceled)